Containing materials in a specified area is a concern in many industrial enterprises. One of the more conspicuous manifestations of containment includes the sequestration of hazardous waste materials. Should such materials escape from the containment facility in which they are impounded, substantial harm could result, both ecologically and economically. To remedy this potential problem, more responsive techniques for detecting leakage from such facilities are needed.
Difficulties that have arisen with regard to leak detection include, inter alia, variations in one or more qualitative characteristics of the material sought to be contained. This makes characteristic specific sensor calibration critical. Another problem is the containment facility can leak from any containment surface or edge and the composition of the container may have to vary because of the material to be contained. Moreover, conditions in the ground surrounding the facility may not necessarily be constant. Thus, monitoring the facility for leakage can be a very resource intensive effort. Various schemes have been offered for remedying one or some of these difficulties in the past. However, the problems persist, and a better leakage detection system is still a highly sought after commodity.
The following prior art reflects the state of the art of which applicant is aware and is included herewith to discharge applicant's acknowledged duty to disclose relevant prior art. It is stipulated, however, that none of these references teach singly nor render obvious when considered in any conceivable combination the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed.
______________________________________ INVENTOR PATENT NO. ISSUE DATE ______________________________________ Berry, J. B. 3,383,863 May 21, 1968 Woods, et al. 4,166,244 August 28, 1979 Johnson, Jr. 4,404,516 September 13, 1983 Kidd 4,644,354 February 17, 1987 Owen 4,905,210 February 27, 1990 Darilek 4,947,470 August 7, 1990 Benson 4,959,639 September 25, 1990 ______________________________________
The patent to Berry teaches the use of a leak detector especially for ponds, tanks or pit liners where the leak is located by a change in electrical resistance around two sets of wires disposed underneath the liner and separated by some previous insulating media. In one form of the invention, liquid from a cavity seeps through a normally impervious coat or liner through a leak such that it will dampen the previous insulating material thus altering the electrical resistance between wires. One limitation of this resistance measuring method is that it has difficulty discerning other present subjacent liquids from those contained in the impoundment. Another limitation is that once a leak does occur, such material may persist in the previous insulating media such that future leaks may not be detected. Another limitation is that only point sources are utilized rather then field sources, limiting this device to leak detection without determining the leak's location. A further limitation is that the relatively fragile bare wires used are subject to potential corrosive and deleterious exposure to material such that these essential wires may be permanently destroyed.
Alternatively, the patent to Woods, et al. teaches the use of an electric field produced by application of current to a metallic reference ring surrounding a tank and a metallic portion of that tank. Leaks from the tank are detected by potential changes in the field as are measured between electrodes placed within the field and the tank. A limitation of this potential variation device is that it is slow, if not incapable in some cases, to detect a leak from the bottom of a tank as opposed to the sides of a tank. A further limitation is that in the form presented, physical attachment to a metallic portion of the tank is required. For applications that do not include a metallic tank attachment, a problem arises.
Likewise, the patent to Johnson teaches the use of a network of electrically conductive wires placed under a reservoir wherein the wires are constructed so that point source only not field source chemicals escaping through a leak will corrode the wires or alternatively degrade the insulation around the wires thereby causing a change in the electrical properties of the wire. One limitation of this system is that should a leak occur, future leak detection may be impossible, due to the necessity of corroding the means of discovering the leak. Another limitation of this system is that it requires actual physical contact of the leaking material and the detecting medium. If the leak is shallow, or if the leak happens to pass between the wires, as opposed to over the wires, the leak will not be detected. A further limitation is that only a point source is utilized as opposed to a field source.
The patent to Kidd teaches the use of an apparatus for detecting the presence of fluid comprised of a sensing means buried on either side of a tank. In particular, the apparatus will indicate whether the condition next to the tank is dry, or whether a polar or non-polar liquid is present. An important limitation of this apparatus is its failure to detect a leak that might occur at the bottom of the tank and continue in a downward direction without ever being detected by the sensing devices next to the tank. Another limitation of the apparatus is that its application has been tailored to predominantly support the peculiarities of a service station environment.
Another patent, issued to Owen, teaches the use of a boat and radio transmitter combination to locate a leak in a liquid impoundment. By use of the radio transmitter the location of the boat can be determined when it detects a leak. A clear limitation of this system would involve the use of a corrosive liquid in the impoundment. Such a liquid would corrode the boat and eventually require its replacement. A further limitation of this system is that radio waves are subject to a myriad of interference problems. Should interference occur, it could lead to leaks either not being detected or being misdetected. Yet another limitation of the system is that when a leak is detected, the migration of the leak cannot be monitored, making remedial efforts far more difficult.
The patent to Darilek teaches the use of an array of electric or magnetic field detectors which are placed on one side of the liner of an impoundment. A voltage is impressed across the liner and the impounded material such that when a leak occurs, a current flows through the leak, creating an electrical field and a magnetic field around the leak whose source can be located geometrically. One limitation of this apparatus is the requirement of locating a voltage impressing electrode in the material impounded. It should be noted that if the impounded material were highly corrosive, the electrode would degrade and need eventual replacement. A further limitation is that if a leak is detected, that leak's further migration cannot be monitored by this apparatus, making remedial measures more difficult.
The Benson patent teaches the use of a flexible rod and sleeve assembly to detect the presence of leaking petroleum. The apparatus detects leaking petroleum on its way toward the water table by being constructed of a material which when contacted by petroleum (but not water) will erode and cause the sleeve to move upward activating an alarm. A clear limitation of this assembly is that the material it is intended or able to detect leaks for is petroleum (or other hydrocarbon materials). This very narrowly tailored invention is designed to detect but one very specific type of leak.